The present invention relates to detection of the fluid pressure in a rotary unit and more particularly to a pressure detector or sensor adapted to deliver an electrical voltage which is a function of the pressure in the unit.
The invention is particularly suitable for use in measuring the pressure in the tire of an aircraft wheel. It is known that a burst or deflated tire may cause an accident on taking off or landing. While a burst tire may be located by visual inspection before the aircraft leaves its parking station, the presence of one or more deflated or under-inflated tires may pass unobserved by the ground personnel. It is consequently desirable to provide an indication on the inflating pressure.
A first consideration of the problem suggests that it may be solved by placing a sensor on the rotary portion of the wheel assembly and transmitting the electrical output signal through a ring and brush system. That solution involves a sliding contact and has drawbacks which are particularly acute in an aircraft wheel due to the temperature variations and the presence of pollutants which requires the use of a sealed system.
It is an object of the invention to provide a detector which is small in size, does not interfere with other devices which may possibly have to be driven by the rotary unit and may easily be rendered fluid-tight.
According to the invention, a pressure detector comprises a non-rotatable housing in which a central shaft for coupling with the rotatable unit is mounted for free rotation while retained against axial movement. The detector further comprises an assembly slidably received on the shaft, connected to the shaft by deformable wall means which define, with surfaces of said assembly, a pressure chamber connectable to the inside of the unit through passage means in the shaft. Said surfaces of the assembly are so constructed that the chamber pressure exerts on the assembly an effective axially directed force which opposes that of a return spring placed between the shaft and the assembly. The assembly may comprise a body of ferromagnetic material variably coupling energizing and receiving windings of a differential transformer carried by the housing. The shape of the ferromagnetic body is such that its axial movement causes variation of the reluctance of the differential transformer and causes a signal to appear at the output of the receiving winding, typically straddled by two energizing windings in the axial direction.
In a particular embodiment, the shaft is provided with radial flanges of different diameters, connected by bellows constituting deformable walls to opposed end surfaces of a disk secured to the movable assembly so as to define surfaces of different effective pressure action areas on the two surfaces of the disk.
If the detector is mounted on an aircraft wheel, the housing will typically be secured to the fixed axle and the shaft will mechanically couple the rotary portion of the wheel and the tachometric generator which is generally necessary, particularly to control an anti-skid braking system.
The invention will be better understood from the following description of particular embodiments, given by way of examples only.